Whole blood is a living tissue that circulates through the heart, arteries, veins and capillaries, carrying nourishment, electrolytes, antibodies, heat and oxygen to the body tissues. Whole blood includes red blood cells (RBCs), white blood cells and platelets suspended in a proteinaceous fluid termed blood plasma. If blood is treated to prevent clotting and permitted to stand in a container, RBCs will settle to the bottom of the container, the plasma will remain on top and the white blood cells will form a layer on top of the RBCs. A centrifuge is commonly used to hasten this separation. The platelet-rich plasma is then removed and placed into a sterile bag for further processing to separate, for example, platelets, clotting factors, albumin, immunoglobulins and the like.
The most important component for the usual transfusion need are the erythrocytes or RBCs, which contain hemoglobin, a complex iron-containing protein that carries oxygen throughout the body and gives blood its red color. The percentage of blood volume that is composed of RBCs is called the “hematocrit.” The average hematocrit in the adult male is 47%. There are about one billion RBCs in two or three drops of blood, and, for every 600 RBCs, there are about 40 platelets and one white blood cell.
Manufactured in the bone marrow, RBCs are enucleated, biconcave discs that are continuously being produced, broken down and destroyed. The biconcave disc shape is crucial to the function of RBCs, presenting a maximal surface area for the capture of oxygen in the lungs and its release in the tissue. The cells are flexible and able to bend in order to traverse the tiny tubules of the capillary beds. Since the cells are enucleated and lack mitochondria, they are unable to carry out cellular repair processes and must rely on anaerobic phosphorylation for energy. After an average of 120 days in the circulatory system, the cells are senescent and are phagocytized by circulating monocytes or the fixed macrophages of the reticulo-endothelial system.
RBCs are prepared from whole blood by removing the plasma. When transfused into a patient, the hematocrit is raised while an increase in blood volume is minimized, which is especially important to such patients as those with congestive heart failure. The cells are typically suspended in about half the original volume; the preparation is referred to as packed red cells. Patients benefiting most from transfusions of RBCs include those with chronic refractive anemia from disorders such as kidney failure, malignancies, gastrointestinal bleeding or acute blood loss as from trauma or surgery.
Because patients seldom require all of the components of whole blood; it is the usual practice in blood banks to separate the blood into components and transfuse only that portion needed by the patient for a specific condition or disease. This treatment, referred to as “blood component therapy” allows several patients to benefit from each unit of blood. Unfortunately, the separation of blood components for therapy is detrimental to the RBCs, causing a storage lesion characterized by a decrease in the marker 2,3-diphosphoglycerate (2,3-DPG), an increase in the production of oxygen free radicals and a change in morphology.
Standard solutions for the storage of whole blood include citrate-phosphate-dextrose solution (CPD) and citrate-phosphate-dextrose-adenine solution (CPDA). Citrate or other anticoagulants such as heparin are necessary to prevent clotting. Because blood is a living tissue that maintains metabolic functions even at refrigerated temperatures, it has been considered necessary to provide an energy source such as dextrose. Phosphate ion can be used to buffer the lactate produced from dextrose utilization.
Improvements in cell preservation solutions over the last 15 years have increased the refrigerated shelf life of whole blood or RBCs from 21 to 42 days. After 42 days, the blood is discarded, since many of the cells have become senescent and would be immediately phagocytized upon transfusion into a recipient. Although the red cells may appear to survive in storage for five or six weeks, they rapidly develop storage lesions characterized by hemolysis and/or biochemical and biomechanical changes that can compromise their survival time and their ability to accept, transport, and unload oxygen to the tissue. For that reason, it is desirable to use the whole blood and blood products within three weeks or less of drawing.
The need remains for a solution in which blood cells in whole blood or packed red cell suspensions can be stored for an increased time and survive functionally when transfused into a recipient. The need also remains for a method to rejuvenate blood and RBCs which are functioning sub-optimally.